1. Field of the Invention
The present invention generally relates to magneto-caloric heating and cooling systems and more particularly to an improved system in which the working material is a continuously circulating paramagnetic fluid.
2. Description of the Prior Art
Magneto-caloric heating and cooling systems transfer heat to and from a paramagnetic working material through the cyclical application and removal of a magnetic field to a paramagnetic working material. The application of the field to the working material under conditions of constant entropy increases its temperature, subsequently allowing heat to be transferred from the material to a high temperature sink. Removal of the field at constant entropy decreases the temperature of the working material and allows subsequent absorption of heat from a low temperature source. Magneto-caloric systems operate around the Curie temperature of the working material and with a proper selection of working material can operate from near absolute zero to near 1400 degrees Kelvin. At temperatures above about 20 degrees Kelvin, for large differences between sink and source temperature it is advantageous to preheat the working material before magnetization and cool the material before demagnetization.
Prior art magnetic heating and cooling systems include reciprocating and rotary designs. In these prior art designs a paramagnetic member is moved in and out of a magnetic field and a fluid flowing through or past the member is used to transfer heat. Examples of such prior art systems are disclosed in U.S. Pat. Nos. 4,727,722; 4,459,811; 4,332,135; and 4,069,028. In general, prior art systems employing solid paramagnetic members as the working material require elaborate seals to prevent leakage of the heat transfer fluid. They are also somewhat inefficient owing to the need for a fluid to serve as a heat transport between the paramagnetic member and the ultimate heat sink and heat source.